Modem aircraft are commonly equipped with one or more active control stick assemblies that permit a pilot to control various aspects of aircraft flight. As a first example, an inceptor-type control stick assembly may be deployed on a fixed wing aircraft and may include a control stick mounted to a gimbal assembly, which permits the control stick to be rotated about two substantially orthogonal rotational axes (i.e., the pitch and roll axes). During operation, one or more positions sensors monitor control stick movement and generate position signals indicative thereof. These position signals are then utilized to carry out corresponding adjustments to the aircraft's pitch and yaw (e.g., by altering the position of movable flight surfaces). As a second example, a collective-type control stick assembly may be deployed on a rotary wing aircraft and may include a control stick mounted to a housing for rotation about a single rotational axis. A position sensor monitors the angular position of the control stick and generates corresponding position signals, which may then be utilized to adjust aircraft lift.
There has been a recent migration in the aircraft industry toward “active” control stick assemblies capable of providing tactile cueing; i.e., haptic force feedback imparted to the control stick indicative of the aircraft's current flight parameters. In general, such active control stick assemblies include at least one artificial force feel (AFF) motor (e.g. a brushless direct current motor) that is selectively energized by a controller. The AFF motor is mechanically coupled to the control stick by a speed reducer, which is conventionally either a gearbox or a harmonic drive. When energized by the controller, the AFF motor drives through the speed reducer to exert a controlled torque on the control stick about one or more of the rotational axes. In this manner, the active control stick assembly generates haptic force feedback, which may be varied by commands from the Flight Control Computers, commensurate with current aircraft attitude and flight conditions.
Although providing the pilot with feedback in a rapid and intuitive manner, conventional active control stick assemblies are limited in certain respects. Active control stick assemblies employing harmonic drive speed reducers impart desirable feel characteristics to control stick movement; e.g., a noticeable smoothness as a pilot rotates the control stick about a rotational axis. However, such control stick assemblies have poor back drive efficiency and consequently may render movement of the control stick excessively difficult in the event of active control failure. By comparison, active control stick assemblies utilizing a gearbox to mechanically couple the AFF motor to the control stick provide little to no backlash; however, such active control assemblies commonly permit the transmission of undesirable forces to the control stick (e.g., vibrations resulting from the meshing of gear teeth within the gearbox), which may negatively impact the overall feel characteristics of the control stick assembly.
Accordingly, it would be desirable to provide an active control stick assembly that exhibits little to no backlash and that imparts desirable feel characteristics (e.g., smoothness) to the movement of the control stick. It would also be generally desirable for such an active control stick assembly to be compact, lightweight, and relatively inexpensive to implement. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended claims, taken in conjunction with the accompanying drawings and this Background.